1) Field of the Invention
The present invention relates to a magnetic recording medium, and more particularly, to a magnetic recording medium including a backing layer which has a very smooth and flat surface and which does not adhere to a magnetic layer when the medium is stored over a long period.
2) Related Art
Recently, as recording density of magnetic recording media is enhanced, the surfaces of their magnetic layers have become more mirror-like, thereby making stable traveling of magnetic tapes difficult. In practice, therefore, a backing layer is provided on the opposite surface of a support with respect to a magnetic layer to ensure stable traveling performance of a magnetic recording medium. In order to prevent a surface-form of the backing layer from being transcribed to the magnetic layer, there is acute need for smoothness of the backing layer itself. However, if the magnetic layer and the backing layer both have smooth and flat surfaces, the two layers adhere to each other after the magnetic recording medium is stored in a wound state for a long time. This phenomenon causes damages to the magnetic layer, so as to lead to increase in dropout and occurrence of jittering of images.
In addition, as portable video cameras have been popular, they have come to be used under a variety of situations such as an outdoor field, etc. As a result, it is necessary to prevent adhesion when the cameras are exposed to severe environments such as high temperature and high humidity over long periods.
To prevent adhesion, addition of a silicone oil is known. However, since the silicone oil generally has poor compatibility with binders, it is liable to cause defects in coating films such as repelling, pin holes, and the like. Proposed is an attempt for improving compatibility between silicone oils and binders by denaturing the silicone oils using fatty acids (JP-A-61-273720). This is effective as long as the compatibility is concerned. However, since the silicone oil and the binder are not fixed to each other, the silicone oil transfers to the magnetic layer when stored in a wound state for a long period. Thus, preventing adhesion does not last long. Furthermore, the silicone oil transferred to the magnetic layer often affects electromagnetic characteristics of the magnetic layer. Another proposal is to use a reaction product of a reactive polysiloxane and a reactive resin. This approach is not successful in achieving sufficient non-adhesion property, because the polysiloxane is taken into the resin so as to hinder molecular orientation of the polysiloxane onto the surface of the backing layer.
The inventors of the present invention have conducted extensive studies to solve the above problems, and they have invented the magnetic recording medium as described below.
An objection of the invention to provide a magnetic recording medium which has a smooth and flat surface.
Another object of the invention is to provide a recording medium which hardly has pinholes nor occurs repelling.
The other object of the invention is to provide a magnetic recording medium having sufficient durability of its backing layer.
A further object of the invention is to provide a paint for producing a backing layer of the above medium.